Disease is one of the main causes of reduced crop yield after harvest. The most common forms of such diseases are fungal and bacterial plant pathogens, such as mold. In citrus fruits, the most common forms of mold are green mold (caused by Penicillium digitatum) and blue mold (caused by Penicillium italicum). In apples, the most common forms of mold are blue mold (caused by Penicillium expansium) and grey mold (caused by Botrytis cinerea).
In order to maximize the amount of post-harvest product, it has become essential to treat the fungal and bacterial pathogens with pesticides and fungicides. Treatment can be accomplished in many different ways, for example, submersion in fungicidal treatment tanks, wrapper impregnation, or fumigation in a containment room. The most common method for applying fungicides is by suspending a fungicide powder in water, then applying the mixture to the fruit with a sprayer.
Since there is a significant cost associated with the application of a fungicide to a product, the harvesting/packaging company must determine whether the cost associated with the fungicidal process can be offset by the anticipated additional yield. As such, it is important to minimize the cost associated with a fungicidal application process.
Synthetic pesticides are utilized quite extensively in all commercial fresh product packing houses to assist in disease treatment. Recently, biological controlling agents were developed for post-harvest use. Biological controlling agents (biofungicides) are living organisms generated to inhibit or eradicate fungi. Since biofungicides are living organisms, they are generally highly susceptible to environmental changes. For example, many biofiungicides are susceptible to temperature changes or exposure to elevated/reduced temperatures for an excessive amount of time. As such, new types of equipment and application techniques are needed to protect the viability of the biofungicides to make their use economically feasible.
One biofungicide commonly used for post-harvest treatment of citrus fruits is Aspire.RTM. (Candida oleophila), sold by the Decco Department of the Agrichemical Division of Elf Atochem North America, Inc, Monrovia, Calif. Decco I-182.RTM. (also Candida oleophila), a biofungicide commonly used for post-harvest treatment of pome fruit, such as apples, is also sold by the Decco Department of the Agrichemical Division of Elf Atochem North America, Inc. These biofungicides are both naturally occurring yeast that is typically supplied as dry, meltable granules in a vacuum packed container. The dry biofungicide is then hydrated and suspended in water prior to use.
Candida cells, such as those present in Decco I-182.RTM. and Aspire.RTM. biofungicide, when packaged in one pound vacuum packed containers (non-suspended) can tolerate heat well. For example, Decco I-182.RTM. and Aspire.RTM. biofungicides are viable at 4.degree. C. for 400-600 days in the original package. When exposed to an elevated temperature of 40.degree. C., Decco I-182.RTM. and Aspire.RTM. bioftingicides remain viable for approximately 5 days in their vacuum packed state. When not in their vacuum packed state, Aspire.RTM. and Decco I-182 .RTM. biofungicides are viable at 4.degree. C. for about 60 days if stored in a dry location.
However, when the Aspire and Decco I-182.RTM. biofungicides are placed in an aqueous suspension at ambient temperature (25.degree. C.), which is the typical application environment, the Candida cells deteriorate rapidly after about 36 hours. As such, the biofungicidal suspension has a shelf life of between about 24 and 36 hours depending on the temperature at which it is stored.
It is conventional in the post-harvest treatment of fruits to prepare sizable batches of the biofungicides in large tanks (e.g., 100 gallons or more) for use during the day to treat harvested product. The biofungicides are prepared by adding biofungicidal powder or granules to water to create a suspension. One pound of Aspire.RTM. or Decco I-182.RTM. biofungicide will treat approximately 20 tons of fruit. A typical mid-sized fruit packing house processes about 30 tons of fruit per hour. Accordingly, between about 12 and 14 pounds of Aspire.RTM. and/or Decco I-182.RTM. biofungicide is utilized in an eight hour day. Typically, a 100 gallon mixture is prepared in a large tank at the beginning of the day and used throughout the day. The benefit to preparing large batches of the suspension is that only one batch preparation is needed, thereby minimizing the stoppage of the fruit treatment process to make additional mixture.
The major drawback in creating large batches of biofungicide is short-term viability of the suspension. If the treatment process is suspended during the day, the remaining portion of the suspension must be used within 36 hours or else the tank contents must be discarded and a fresh batch made when treatment resumes. It has been quite common to have to dispose of up to 25% of a batch (i.e., 25 gallons) because it has exceeded its useful life. Also, since it is impossible to predict the actual run time in a fruit packing house, additional batches of biofungicidal mixture must sometimes be prepared during the day. The costs associated with discarding the non-viable biofungicide and the time required to prepare new batches of biofungicide mixture are quite significant.
A need, therefore, exists for a system for preparing biofungicidal suspensions for treating harvested fruits which minimizes wastage during shutdown and which does not delay the treatment process.